Method of instrument standardization for a spectroscopic device

ABSTRACT

In a spectroscopic process a sample for producing a test spectral line or spectrum of at least one component contained in the sample is stimulated and the transmitted and/or emitted electromagnetic rays are used to create the test spectral line or spectrum. In order to improve such a spectroscopic process to such an extent that variations of certain parameters, which alter the shape and/or occurrence of a spectral line, are compensated, a comparison spectral line or spectrum of a known comparison material is produced under substantially the same parameters as the sample. The comparison spectral line or spectrum is compared with an ideal comparison spectral line or spectrum in order to calculate a transfer function, and the transfer function is applied to the test spectral line or spectrum in order to calculate a corrected test spectral line or spectrum.

FIELD OF THE INVENTION

The present invention relates to an improved method of standardizationfor a spectroscopic device, and more particularly to such a method ofstandardization which corrects for variations of certain parameterswhich may alter the shape and/or occurrence of a spectral line.

BACKGROUND OF THE INVENTION

The invention relates to a spectroscopic process whereby, in aspectroscopic device, at least one sample for producing a test spectralline or spectrum of at least one component contained in the sample isstimulated and the transmitted and/or emitted electromagnetic ray isconducted through an optic system, possibly with a spectrometer, of adetector device in order to record the test spectral line or spectrum.

Such a spectroscopic process is common, for instance, in atomicabsorption spectroscopy. There, a corresponding sample is vaporized, forinstance in a graphite furnace, and the vaporized sample is stimulatedby monochromatic or continuously electromagnetic radiation. With atomicabsorption spectroscopy, part of the electromagnetic radiation isabsorbed by at least one component of the sample. Absorption of theelectromagnetic ray thus corresponds to a stimulation of the component.Because the absorbed ray is absent in the transmitted electromagneticray, there is a corresponding spectral line, which is characteristic forthe corresponding component of the sample. The transmittedelectromagnetic ray in the spectroscopic process and also in the atomicabsorption spectroscopy is conducted in the direction of a detectordevice by means of an optic system and possibly through the use of aspectrometer. The detector device serves to record the test spectralline, which is characteristic for the absorption, by the correspondingcomponent of the sample. If a continuous electromagnetic ray is used,then an entire test spectrum can also be recorded. Hereafter, the term“spectral line” is used, although it should be understood that this termis also meant to encompass the situation where an entire “spectrum” isrecorded.

A disadvantage of the spectroscopic process known in general practice isthat changes, for instance of certain parameters such as temperature,pressure, and so on, which can result in a modification of the testspectral line are not recorded and can result in a displacement of, andpossibly also a change in the intensity of, the spectral line. As aresult, in an extreme case, with closely situated spectral lines ofvarious components of a sample, misdiagnosis can occur concerning atleast one of these components. In addition, even with correctcoordination of the spectral lines with respect to a certain componentof the sample, the result can be various spectral lines at variouspoints of measurement for various spectroscopic devices on various dayswith the same component.

The invention therefore is concerned with improving a spectroscopicprocess of the aforementioned type to such an extent that variations ofcertain parameters, which alter the shape and/or occurrence of aspectral line, are compensated, so that, independently of modificationsof these parameters, an ideal test spectral line is received.

SUMMARY OF THE INVENTION

In keeping with the invention, a comparison material is used along withthe sample. A corresponding comparison spectral line is provided forthis comparison material. This comparison spectral line is subjected toa modification in shape and position in the wavelength or frequencyrange, if changes are made in corresponding parameters, such astemperature, pressure, mechanical wear of the spectroscopic device, thesetting of the spectroscopic device, points of measurement, or the like.For the comparison spectral line an ideal comparison spectral line isknown, based on prescribed standard values of the parameters. Theprescribed standard values correspond, for example, to a particulartemperature, a particular pressure, a particular condition of thespectroscopic device, or the like. By comparing the measured comparisonspectral line and the ideal comparison spectral line, a transferfunction is obtained from both. This function corresponds to amathematical filter, which, where software is concerned for instance, isapplied to corresponding spectral lines and especially to the measuredtest spectral line. By using the transfer function, one receives fromthe test spectral line an ideal test spectral line, which results in anideal test spectral line that is comparable in simple manner with thespectral detection, independently of the real existing parameters in thespectral investigation.

As already stated, the spectroscopic process according to the inventioncan also be used on corresponding spectrums as a whole. In addition, itis also possible to obtain a corresponding spectral line or spectrum forradiation emitted by the corresponding component. In this case as well,the foregoing statements also apply.

To obtain simplified access to the component or components of thesample, the sample is brought into its gaseous state before it isstimulated. Depending on the comparison material in use, it too isvaporized.

To simplify the spectroscopic process, samples and comparison materialcan be vaporized, stimulated, and/or spectrally examined in the samespectroscopic device. In the simplest case, not just vaporization butstimulation as well as spectral examination occurs in the samespectroscopic device, so that all the various parameters of thespectroscopic device can be taken into account in simple manner throughthe transfer function. If, for instance, the vaporization or stimulationor spectral measurement occurs in various spectroscopic devices, furthertransfer functions may be necessary in order to take into account thevarious parameters of the various spectroscopic devices.

To simplify the spectroscopic process still further and to improve itsreproduceability and the use of the transfer function, the sample andcomparison material can be vaporized, stimulated, and/or spectrallyexamined simultaneously. If everything is carried out simultaneously forthe sample and comparison material, the transfer function also takesinto account all variants in the parameters of the spectroscopic deviceand/or of the spectroscopic process. For instance, if the stimulation ofthe sample and comparison material do not occur simultaneously, aresidual error could possibly remain, through the reported transferfunction, in the stimulation of the sample and the comparison material.However, these errors can be so minor that any delayed vaporization orspectral examination of the sample and comparison material can betolerated.

Depending on the detector device in use with the detector attachment, itmay be necessary for the sample and comparison material to be spectrallyexamined separately, in particular at a certain time interval. This isacceptable if the parameters for the period of the spectral examinationof the sample and comparison material, parameters which can possiblyalter the spectral examination, are altered only to a minor extent ornot at all.

However, in order to be able to conduct a spectral examinationsimultaneously, the detector device can have two detector attachments,one of which spectrally examines the sample while the other examines thecomparison material. A corresponding optic system with spectrometers canresult, for instance, in a splitting of the electromagnetic ray of thesample and the comparison material so that in each case thecorresponding electromagnetic ray falls onto the related detectorattachment.

It is theoretically possible also to investigate the corresponding testfunction with unknown comparison material, if this material for instanceis always an additional component of the sample. If the spectral line ofthis comparison material is easy to examine, then corresponding changesin shape and length of the spectral line can also be recorded and acorresponding transfer function can be applied to these modifications.This transfer function can also be applied to the relevant component ofthe sample.

If the comparison material is known, then associated with it there is anideal comparison spectral line, which can be stored in the spectroscopicdevice or in an analytical device attached thereto. By comparing themeasured comparison spectral line with the ideal comparison spectralline, the corresponding transfer function can be investigated. This canoccur automatically by means of corresponding software. Then theinvestigated transfer function is applied to the test spectral line andin this manner an ideal test spectral line is received.

If, for instance, the temperature varies between different readings ofthe spectral line of a particular component of the sample, this mayresult in a wavelength/frequency modification of the test spectral line.The transfer function can compensate for such wavelength/frequencymodification and thus also for the temperature variation.

A temperature change, however, can also modify a line thickness in thespectroscopic device, so that the resolution of the spectroscopic devicechanges. Such a change can also be compensated by a correspondingtransfer function.

One example of a simple and reasonably priced comparison material, whichis not required to be vaporized at customary temperatures in the atomicabsorption spectroscopy, is neon. This comparison material shows arelatively simple spectral line at 296.72 nm, which can serve well toconvey corresponding transfer functions. However, other comparisonmaterials and/or other orders of spectral lines of neon or othercomparison materials can also be used. Neon is also desirable due to thefact that it, like helium, argon, krypton, xenon and radon, is an inertgas which does not readily react with most other materials.

If a number of measurements have already been taken with the samecomparison material, it is also possible that a series of comparisonspectral lines can be stored in the analytic device of the electroscopicdevice, especially for different parameters. By comparing the storedcomparison spectral line with a comparison spectral line that hasactually been newly recorded, a corresponding transfer function can beexamined and applied on a test spectral line. In this case, the resultfor the test spectral line is a new test spectral line which correspondsto the stored spectral line which has been called up. As a result, it ispossible to make comparisons between spectral lines recorded withdifferent parameters without deriving the recorded spectral lines fromideal spectral lines.

It is possible to break down the parameters roughly into two groups. Onegroup are the measurement parameters, which for instance correspond tophysical values such as temperature, pressure, or the like. The othergroup are the device parameters, which result from different degrees ofmechanical wear of the spectroscopic device, various settings, variousplaces of construction, or the like. Through this invention, it ispossible to determine transfer functions separately for variations inthe measurement parameters and the device parameters, and to apply themaccordingly to the test spectral lines.

The invention and its particular features and advantages will becomemore apparent from the following detailed description considered withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a spectroscopic device for conducting thespectroscopic standardization process of the invention, with specialemphasis on the detector device and the analytic device;

FIG. 2 is a graphical representation showing a series of comparisonspectral lines at various temperatures which may be produced by thespectroscopic device of FIG. 1;

FIG. 3 is a graphical representation showing an ideal comparisonspectral line at various temperatures which may be produced by thespectroscopic device of FIG. 1;

FIG. 4 is a graphical representation showing a series of transferfunctions for various temperatures as variable parameters which may beused by the spectroscopic standardization process employed by thespectroscopic device of FIG. 1;

FIG. 5 is a graphical representation showing a series of test spectrallines for the same temperatures as in the comparison spectral linesaccording to FIG. 2 which may be produced by the spectroscopic device ofFIG. 1; and

FIG. 6 is a graphical representation showing an ideal test spectral linecompensated by means of a transfer function with respect to temperaturevariations which may be produced by the spectroscopic device of FIG. 1.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Shown in FIG. 1 are a detector device 2 and an analytic device 9 of aspectroscopic device 1, which serves to conduct the spectroscopicprocess of this invention. For purposes of simplification, and becausesuch elements are well known in the art, the illustration does not showfeatures such as a monochromatic ray source for instance, a vaporizationfurnace, and an optic system that may include a spectrometer.

The detector device 2 has two detector attachments 7, 8. The upperdetector attachment 7 shown in FIG. 1 serves to investigate a comparisonspectral line for a comparison material. The lower detector attachment 8in FIG. 1 serves to investigate a spectral line of a component of asample, where the sample and comparison material are vaporizedsimultaneously, stimulated by electromagnetic ray, and spectrallyinvestigated. Vaporization and stimulation ensue in the non-illustratedportion of the spectrometer, which may be for example an atomicabsorption spectrometer or an optical emission spectrometer.

An ideal comparison spectral line is stored, for instance, in analyticalunit 9. FIG. 3 shows an example of this. The abscissa of the graph plotsthe wavelength or frequency and the ordinate plots the intensity. Theideal comparison spectral line 5, according to FIG. 3, is a spectralline of neon at 296.72 nm at particular ideal temperature conditions.However, if the temperature of the spectroscopic device, of the opticsystem, and/or of the detector unit 2 varies, then the result can be adisplacement of the spectral line. Comparison spectral lines 4 displacedin this way are shown, for instance, in FIG. 2. This leads to adisplacement toward the right, that is, to high wavelength andsimultaneously a decrease in intensity with increasing temperaturevalues.

Comparison of the ideal comparison spectral line 5 in FIG. 3 with acomparison spectral line 4 actually recorded at a certain temperaturevalue leads to a so-called transfer function or a filter function (ƒ), anumber of which are illustrated in FIG. 4 with reference number 6 forthe various temperature values of FIG. 2. In this case the transferfunctions 6 are shown successively as dependent on various temperaturevalues. Thus:R*ƒ=R ₀wherein

-   -   ƒ is the unknown transfer function or filter function,    -   R₀ is the ideal comparison spectral line 5 in FIG. 3, and    -   R is the comparison spectral line 4 in FIG. 2 actually recorded        at a certain temperature value.

Thus, an ideal comparison spectral line (R₀) can be determined byconvoluting a known comparison spectral line (R) with a known transferfunction or filter function (ƒ). Similarly, an unknown transfer functionor filter function (ƒ) can be determined by deconvoluting a knowncomparison spectral line (R) out of a known ideal comparison spectralline (R₀). Use of a corresponding transfer function (ƒ) on a relatedcomparison spectral line 4 according to FIG. 4 leads to an idealcomparison spectral line 5 according to FIG. 3.

The transfer function (ƒ) received in this way is also applied to acorresponding test spectral line, which was provided by the detectorattachment 8 of FIG. 1 for the corresponding component of the sample.Various test spectral lines 3 for various temperature values are shownin FIG. 5, where these temperature values correspond to those in FIG. 2and there is a corresponding transfer function 6 according to FIG. 4 isassociated to each of these temperature values. The application of therelated transfer functions 6 to the test spectral lines 3 according toFIG. 5, where the transfer function is selected corresponding to thetemperature value, leads to an ideal test spectral line 10 according toFIG. 6. Thus:A*ƒ=A ₀wherein

-   -   A₀ is the unknown ideal test spectral line 10 according to FIG.        6,    -   ƒ is the transfer function or filter function, and    -   A is the test spectral line 3 according to FIG. 5.

In this connection, it is important to note that the foregoingdiscussion, in order to simplify the description, deals only withtransfer functions 6 that depend on the temperature value, wherecorresponding displacements of the spectral lines and shape changes,that is, modifications in the intensity of the spectral lines, arosethrough differences in temperature values. If other parameters in thespectroscopic device, such as pressure, mechanical wear of the device,set-up location of the device, or the like, are changed, other transferfunctions can be obtained, which take into account the variation of allthese parameters including variation of the temperature and serve tocompensate these modifications. The compensation ensues in such a way asto compensate for certain pre-established values of the parameters,where these values of the parameters determine the corresponding idealspectral lines according to FIGS. 3 and 6.

Use of the transfer function leads to an improved comparison possibilityfor spectral lines, which were recorded at various times at variousplaces by various people and the like. Variations of spectral lines onthe basis of corresponding variations of parameters in measurement arecompensated by the transfer function, so that in every case a comparisonof the measurement results is possible in a safe and simple way,independently of the aforementioned parameters.

Although the invention has been described with reference to a particulararrangement of parts, features and the like, these are not intended toexhaust all possible arrangements or features, and indeed many othermodifications and variations will be ascertainable to those of skill inthe art.

1. A method of standardization for a spectroscopic device comprising thesteps of: providing a detector having a first attachment and a secondattachment; simultaneously stimulating a sample and a comparisonmaterial; producing a first signal indicative of a test spectral line orspectrum of at least one component contained in the sample using thefirst attachment; producing a second signal indicative of a comparisonspectral line or spectrum of the known comparison material using thesecond attachment; comparing the second signal indicative of thecomparison spectral line or spectrum produced using the secondattachment with an ideal comparison spectral line or spectrum tocalculate a transfer function; and, applying the transfer function tothe test spectral line or spectrum to calculate a corrected testspectral line or spectrum.
 2. The method according to claim 1 furthercomprising the step of converting the sample and the comparison materialinto a gaseous condition before said producing steps.
 3. The methodaccording to claim 2 wherein the sample and the comparison material arevaporized, stimulated, and spectrally investigated in the samespectroscopic device.
 4. The method according claim 3 wherein the sampleand the comparison material are simultaneously vaporized.
 5. The methodaccording to claim 1 wherein the ideal comparison spectral line orspectrum is stored in the spectroscopic device or in an examinationdevice relating to it and is retrieved for the calculation of thetransfer function.
 6. The method according to claim 1 wherein thetransfer function is applied to the test spectral line or spectrum tocompensate for a wavelength or frequency modification.
 7. The methodaccording to claim 1 wherein the transfer function is applied to thetest spectral line or spectrum to compensate for a resolutionmodification of the spectroscopic device.
 8. The method according toclaim 1 wherein neon is used as the comparison material.
 9. The methodaccording to claim 1 wherein a series of comparison spectral lines orspectrums for various parameters are stored, and wherein, through acomparison with a comparison spectral line or spectrum that was actuallyrecorded, a corresponding transfer function is obtained from the storedspectral lines or spectrums and retrieved for application to the testspectral line or spectrum.
 10. The method according to claim 1 whereinthe transfer function is applied to the test spectral line or spectrumas determined for variation of measurement parameters and deviceparameters.
 11. The method according to claim 1 wherein the transferfunction is applied to the test spectral line or spectrum as determinedfor variation of measurement parameters.
 12. The method according toclaim 1 wherein the transfer function is applied to the test spectralline or spectrum as determined for variation of device parameters.
 13. Aspectroscopic process whereby, in a spectroscopic device having adetector with a first attachment and a second attachment, at least onecomponent contained in a sample is stimulated and a first signalindicative of a test spectral line or spectrum of the at least onecomponent in the sample is produced using the first attachment,characterized in that, a comparison material is stimulated,simultaneously with the at least one component in the sample, and asecond signal indicative of a comparison spectral line or spectrum isproduced using the second attachment, a transfer function is obtainedfor the known comparison material by using the second signal indicativeof the comparison spectral line or spectrum produced using the secondattachment, which transfer function translates the comparison spectralline or spectrum into a corrected ideal comparison spectral line orspectrum, and the transfer function is applied to the test spectral lineor spectrum.
 14. A spectroscopic process according to claim 13,characterized in that the sample and the comparison material areconverted into a gaseous condition before stimulation.
 15. Aspectroscopic process according to claim 14, characterized in that thesample and the comparison material are vaporized, stimulated, andspectrally investigated in the same spectroscopic device.
 16. Aspectroscopic process according claim 15, characterized in that thesample and the comparison material are simultaneously vaporized.
 17. Aspectroscopic process according to claim 13, characterized in that theideal comparison spectral line or spectrum is stored in thespectroscopic device or in an examination device relating to it and isretrieved for the provision of the transfer function while thecomparison spectral line or spectrum is in use.
 18. A spectroscopicprocess according to claim 13, characterized in that the transferfunction is applied to the test spectral line or spectrum to compensatefor a wavelength or frequency modification.
 19. A spectroscopic processaccording to claim 13, characterized in that the transfer function isapplied to the test spectral line or spectrum to compensate for aresolution modification of the spectroscopic device.
 20. A spectroscopicprocess according to claim 13, characterized in that neon is used ascomparison material.
 21. A spectroscopic process according to claim 13,characterized in that a series of comparison spectral lines or spectrumsfor various parameters are stored, and that, through a comparison with acomparison spectral line or spectrum that was actually recorded, acorresponding transfer function is obtained from the stored spectrallines or spectrums and retrieved for application to the test spectralline or spectrum.
 22. A spectroscopic process according to claim 13,characterized in that the transfer function is applied to the testspectral line or spectrum as determined for variation of measurementparameters and device parameters.
 23. A spectroscopic process accordingto claim 13, characterized in that the transfer function is applied tothe test spectral line or spectrum as determined for variation ofmeasurement parameters.
 24. A spectroscopic process according to claim13, characterized in that the transfer function is applied to the testspectral line or spectrum as determined for variation of deviceparameters.